We use the Exponential Weighted (EW) historical volatility that assigns bigger weights to the recent returns, and smaller weights to the past ones. The EWHV is more responsive than the equally weighted historical volatility. Also, the decline of the EWHV from its peak is smoother than that of the equally weighted HV.

http://tech.harbourfronts.com/exponentially-weighted-historical-volatility-in-excel-volatility-analysis-in-excel/